Recently, printers as terminal recording apparatuses in the field of information communications are being strongly required more and more to be of smaller size and capable of higher-rate printing and color printing. Because of this, electrophotographic photoreceptors for use in electrophotographic laser beam printers or LED printers have come to be required to be of even smaller size and capable of coping with a higher printing rate.
In order to obtain such an excellent electrophotographic photoreceptor, it is, of course, necessary to employ a charge-generating substance and a charge-transporting substance each having satisfactory properties. Besides this, it is also important that the injection of charge carriers from the charge-generating substance into the charge-transporting substance, i.e., the injection of charges from a charge-generating layer into a charge-transporting layer, should be efficiently conducted. Since this charge injection depends on the properties of the interface between the charge-generating substance (or charge-generating layer) and the charge-transporting substance (or charge-transporting layer) and varies with combinations of various substances, charge-transporting substances having a variety of properties are being developed.
N,N'-Diphenyl-N,N'-bis(3-methylphenyl)-4,4-biphenylenediamine (4) is already known to effectively function as a charge-transporting material (see JP-B-58-32372 (the term "JP-B" as used herein means an "examined Japanese patent publication") and U.S. Pat. No. 3,265,496).
Several diaminobiphenyl compounds also are known as charge-transporting materials (see JP-B-63-6864, JP-B-5-40904, Japanese Patent 2,539,641, EP 0648737 A1, JP-A-6-199745 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-6-293716, JP-A-7-188130, JP-A-7-181693, and U.S. Pat. No. 5,399,453).
Electrophotographic photoreceptors are known which employ a mixture of a diaminobiphenyl compound having two or more alkoxy groups on the same aromatic ring and other charge-transporting material(s) (see JP-A-7-225486, JP-A-6-342215, JP-A-6-342220, JP-A-6-342218, JP-A-6-342217, JP-A-6-342216, JP-A-5-341545, and JP-A-5-341544).
Combinations of a diaminobiphenyl compound and a binder polymer are known (see JP-A-7-120941, JP-A-6-214412, and JP-A-6-130685).
Also known are combinations of a diaminobiphenyl compound and a charge-generating material (see JP-A-6-75408, JP-A-6-161132, JP-A-6-75403, JP-A-5-257310, JP-A-5-188615, JP-A-5-281769, and JP-A-5-257309).
Applications of m-diaminobenzene derivatives to materials for electrophotographic photoreceptors are described, e.g., in JP-A-1-142642 and JP-A-5-88389. An m-diaminobenzene derivative having a fluoroalkyl group bonded to the central benzene ring is described in JP-A-7-126224, and an electrophotographic photoreceptor employing this derivative is described in JP-A-1-128880. JP-A-3-105347 discloses an m-diaminobenzene derivative having a thiocarbonyl group. An m-diaminobenzene derivative having a methoxy group and a phenyl group bonded as substituents to the central phenyl group is described in JP-A-2-93653, and an electrophotographic photoreceptor employing this derivative is described in JP-A-2-93654. In JP-A-5-58966 and JP-A-5-301848 are disclosed m-diaminobenzene derivatives in which one of the amino groups is substituted with a pyrene ring. JP-A-4-300853 discloses a diaminobenzene derivative having an olefin substituent and an electrophotographic photoreceptor employing this derivative. Furthermore, an electrophotographic photoreceptor employing a diaminobenzene compound having three or four amino substituents in the molecule is disclosed in JP-A-3-94258 and JP-A-3-94259.
As described above, electrophotographic photoreceptors employing a compound selected from many diaminobiphenyl or diaminobenzene compounds have been proposed. However, these compounds have drawbacks that they are apt to separate out as crystals because of their insufficient solubility, have poor miscibility with binder polymers, and are insufficiently compatible with phthalocyanines suitable for use as charge-generating materials. Consequently, there have been cases where the prior art electrophotographic photoreceptors have insufficient photosensitivity or have a high residual potential to cause scumming.